Collapsible container

ABSTRACT

A collapsible container formed from a cut and scored blank of paperboard or similar foldable sheet material which, when set up, provides a tubular body having an open top with a circular cross section and a bottom wall structure which comprises panels integrally hinged along straight lines to the bottom edge of the tubular body, which panels are connected in pairs and are automatically foldable inwardly between the body side wall forming panels when the latter are collapsed and which, when the container is opened up, have interlocking portions adapted to hold the bottom wall panels in an upwardly directed cone-shaped formation, thereby providing a support for the container contents which has a degree of resiliency.

nited States Patent [191 a Arneson 1 Aug. 6, 1974 [54] COLLAPSIBLE CONTAINER 3,526,352 9/1970 Swett 229/39 R 3,713,576 1/1973 Goebel 229/38 [75] Inventor: Edwin L. Arneson, Hillsdale, NJ.

[73] Assignee: Federal Paper Board Company, Inc.,

Montvale, NJ.

22 Filed: Apr. 10,1972

[21 Appl. No.: 242,623

[52] US. Cl. 229/39 R, 229/21, 229/41 C [51] Int. Cl 865d 5/10, B65d 3/04 [58] Field of Search 229/21, 41 R, 41 B, 41 C,

Primary Examiner-William 1. Price Assistant Examiner-Stephen Marcus Attorney, Agent, or Firm-Guy A. Greenawalt [5 7] ABSTRACT A collapsible container formed from a cut and scored blank of paperboard or similar foldable sheet material which, when set up, provides a tubular body having an open top with a circular cross section and a bottom wall structure which comprises panels integrally hinged along straight lines to the bottom edge of the tubular body, which panels are connected in pairs and are automatically foldable inwardly between the body side wall forming panels when the latter are collapsed and which, when the container is opened up, have interlocking portions adapted to hold the bottom wall panels in an upwardly directed cone-shaped formation, thereby providing a support for the container contents which has a degree of resiliency.

10 Claims, 8 Drawing Figures 1 COLLAPSIBLE CONTAINER This invention relates to packaging and is more particularly concerned with improvements in a collapsible container which is adapted to be formed of connected panels of paperboard or similar material and which has a generally cylindrical shape, when set up, with bottom forming panels which are foldable for disposition between the side wall panels when the container is collapsed.

Containers have been designed for packaging products of various kinds which comprise a cylindrical body, initially open at both ends, with a pair of axial scores so that it may be collapsed into flattened condition for shipment and adapted to be opened up to receive top and bottom closures comprising circular discs held within annular rims, generally of metal, which engage collars on the ends of the tubular body to hold the top and bottom closure discs in position. Another form of container of this general type which has been developed recently and which is illustrated in U.S. Pat. Nos. 3,269,640 and 3,4l1,692 comprises a cylindrical body, when set up, which is circular at the top for receiving a circular closure member and which has a side wall of generally cylindrical shape throughout the major portion thereof and a bottom wall forming an end closure which extends in a transverse plane and which has a periphery defined by a multiplicity of straight edges, each hinged to a generally flat faced web section in the bot- I tom margin of the side wall, which web section merges into the upper cylindrical shape of the sidewall. The bottom wall comprises panels which are hinged to the side wall and foldable so as to collapse between the side wall forming panels when the container is collapsed and to automatically open up into end or bottom wall forming relation when the side wall panels are opened up.

It is a general object of the invention to provide an improved container of generally cylindrical shape which is fabricated from a blank of paperboard, or like material, by cutting and scoring the same to provide side wall forming panels and bottom wall forming panels which are adapted to be connected so as to form, initially, in a knocked down condition, a container body which is adapted to open up into generally cylindrical form and a bottom end wall structure formed of a plurality of panels hinged to the bottom edges of side wall panels and folded between the side wall panels, which bottom wall panels automatically open into end wall forming relation when the container is set up.

It is a more specific object of the invention to provide a container which is adapted to be fabricated from a cut and scored blank having a series of hingedly connected panels which are joined so as to form a collapsible, generally cylindrical container body, when opened up, and which has side walls of generally cylindrical shape throughout the major portion thereof and a bottom wall forming end closure having a periphery defined by a plurality of straight edges each hinged to a generally flat faced web section in the bottom margin of the side wall which web section merges into the cylindrical shape of the side wall, the bottom end wall being constructed so that the panels thereof have interlocking portions when opened up which are so constructed that the bottom wall will form a cushion for supporting the contents of the container with a substantial amount of resiliency.

It is a further object of the invention to provide a generally cylindrical container which is collapsible into flattened condition and closed at one end by a series of hingedly connected panels, which panels are interleaved and connected so as to fold upon each other between the collapsed side wall forming panels in the flattened condition thereof and, when the container is opened up, having a periphery which is hexagonal, with straight edge portions hinged to the bottom edges of flat faced side wall sections on straight hinge lines and with side wall sections merging into the main body of the side wall on generally semi-circular lines, and the bottom wall panels having interlocking portions for holding the same in an upwardly extending coneshaped contour, therey affording a certain degree of resiliency and protecting the contents, which may be fragile, against damage when the container is deposited on a supporting surface.

These and other objects and advantages of the invention will be apparent from a consideration of the container and the method of forming the same which is shown by way of illustration in the accompanying drawings wherein:

FIG. 1 is a perspective view of a container body in set up condition which embodies therein the principles of the invention;

FIG. 2 is a vertical section taken on the line 2-2 of FIG. 1, the view showing the top closure lid in position for application to the open top of the container;

FIG. 3 is a horizontal section taken on the line 33 of FIG. 2;

FIG. 4 is a bottom plan view with the container in partially opened up position;

FIG. 5 is a plan view of flexible paperboard blank employed in fabricating the container, the view illustrating the manner in which the blank is died out and creased;

FIG. 6 is a plan view of the blank of FIG. 5 following initial folding of certain bottom forming members thereof and showing the application of glue prior to further folding operations;

FIG. 7 is a plan view of the completed container in flattened down condition; and

FIG. 8 is a fragmentary plan view showing a portion of the flattened container and having portions broken away so as to expose certain of the bottom closure or end wall forming panels.

The container will be best understood by reference to the preferred manner in which it is formed and set up. Referring first to FIG. 5, the improved container is fabricated from a flat blank 10 of flexible paperboard of suitable gauge or thickness, or similar foldable sheet material. The blank 10 is subdivided by parallel, transverse crease lines 11 and 12 into successive, integrally hinged wall forming panels 15, 16 and 17 which constitute the main portion of the blank and which are adapted to form the generally cylindrical side wall of the container body when set up. A'narrow edge reinforcing flap 18 extends along the side margin of the blank and is adapted to hinge inwardly about the longitudinal crease line 13 so as to fold down and be secured against the adjacent outside face thereof. A longitudinal crease line 14 defines the bottom edge of the side wall forming panels l5, l6 and 17 and forms a hinge line for a series of bottom wall or end closure forming panels which extend laterally of the main portion of the blank and the longitudinal crease line 14.

The bottom wall forming panels have hinge forming edges which are of equal length and which extend along the crease line 14 so as to define in the finished and set up carton six straight edges of equal length. The bottom wall forming panels are cut and creased so that they may be connected in pairs. The one panel of the larger pair thereof, in the form of the blank shown, is a generally rectangular panel 20 which extends from the center of the side wall panel 16 and which is hinged to the latter along portion 21 of the score line 14. Panel 20 has an outer marginal portion 22 with triangular hook formations 23 and 23' at opposite ends in the direction of the length of the blank 10. The marginal portion 22 is subdivided by a crease line 24 which bisects the hook formations 23 and 23'. The hook formations 23 and 23 extend outwardly of the side edges 25 and 25 of the panel 20. The outermost portion 26 of the marginal panel portion 22 constitutes a glue tab for connection with an outer marginal portion of the rectangular panel 27 which extends outwardly of the panel 17 near the terminal edge of the blank 10. The panel 27 has a dimension between the hinge forming portion 28 of the crease line 14 and the outer edge 29 which corresponds approximately to the dimension of the panel 20 between the hinge portion 21 of crease line 14 and the score line 24. A generally triangular shaped panel or flap 30 extends from the panel 16 at one side of the bottom panel 20 and is hinged to the panel 16 along the portion 31 of the crease line 14. At the opposite side of the panel 20 the flap or panel 32 is hinged to the panel 16 along portion 33 of the crease line 14. The panels 30 and 32 are separated from the panel 20 by outwardly opening, generally V-shaped slots 34 and 35 which extend from the ends of the hinge line 21. The panel or flap 32 is subdivided by crease or score line 36 which divides the panel into two substantially equal, generally triangular panels which are foldable upon each other about the crease line 36. The outer edge of the panel 32 is cut on a curved line 37 which rounds into a connection with the end of a straight inner edge line 38 extending diagonally outwardly of the intersection of the transverse score line 12 with the longitudinal crease line 14. A locking aperture 39 for co-operation with the locking tongue 23 is formed in the panel 32 by a semi-circular cutting line 40, the ends of which terminate at straight cutting lines 41, and 41 the latter being disposed at an angle to each other and straddling the score line 36 upon which the two sections of this panel are adapted to be folded. An adjoining glue tab panel 42 of generally triangular shape extends outwardly of the side wall panel 17 and is hinged to the bottom forming edge thereof on a hinge line 43 constituting a portion of the longitudinal crease or score line 14 and extending approximately half the length of the panel 17 in the longitudinal direction of the blank. The panel 42 is separated from the panel 32 by a narrow outwardly opening triangular slot 44 and from the adjoining panel 27 by a triangular shaped slot 45. At the other end of the blank there extends laterally of the blank a panel 52 which is adapted to hinge on the portion 53 of the crease line 14 and which has the same shape and approximately the same dimensions as the panel 32. The panel 52 is subdivided by crease or score line 56 into two substantially equal generally triangular panels which are foldable on the crease line 56. The outer edge 57 of the panel 52 is cut on a curved line which extends to and joins the outer end of a straight inner edge line 58. Panel 52 is provided with a latching aperture 59 for co-operation with latching tongue 23 which is formed by a half circle cutting line 60 with the ends terminating at angularly related cutting lines 61 and 61', the aperture and the cutting lines straddling the hinge forming score line 56. The panel or tab member 52 is separated from the adjoining glue tab panel member 30 by an outwardly opening V-shaped slot 64.

A generally semi-circular score or crease line 65 extends into the panel 15 with the ends terminating at the ends of the hinge line 53. The upwardly or inwardly curved or bowed score line 65 and the cord-like hinge line 53, which constitutes a portion of crease line 14 and the bottom forming edge of the side wall forming panel 15, together define a web section integrally connecting the bottom wall panel 52 to the side wall panel 15. Similar score lines 66, 67, 68, 69 and 70 extend into the panels 16 and 17 along score line 14 with their ends terminating at the ends of the hinge lines 31, 21, 33, 43 and 28, respectively. The score lines 65, 66, 67, 68, 69 and 70 are substantially identical in character and extend the same distance into the panels 15, 16 and 17 and define with the hinge lines 53, 31, 21, 33, 43 and 28 web sections indicated at 71, 72, 73, 74, and 76.

To complete the container from the blank of FIG. 5, glue is applied and the panels are folded as illustrated in FIGS. 6, 7 and 8. Initially, the edge reinforcing flap 18 may have glue applied to its face so that it can be folded back onto the main body of the panels 15, 16 and 17, and secured thereto to form an outer reinforcing rim around the mouth of the completed container. The panels 20, 27, 30, 32, 42 and 52 are all folded onto the inside face of the main portion of the blank 10 about their respective hinge lines 21, 28, 31, 33, 43 and 53 so as to bring these panels into the position shown in FIG. 6, the glue flaps 26, 32 and 52 being folded back on the score lines 24, 36 and 56. Glue is applied to the flap members 26, 30 and 42 and to the flap forming marginal portion 77 of the wall panel 17 as indicated in FIG. 6. The wall panels 15 and 17 are then folded about the score lines 11 and 12, respectively, so as to bring the glued portion 77 of the panel 17 into overlapping relation with a marginal end portion of the panel 15. This completes the fabrication of the container which, in the knocked down condition, appears as in FIG. 7.

The container is set up by applying force to the edge folds 11 and 12 in the direction of the center of the assembly which causes the side wall forming panels to open up into generally cylindrical shape with the bottom wall forming panels automatically pulled by the opening of the side wall panels into end closing position so as to constitute an end wall as shown in FIGS. 2 and 3. The bottom wall panels hinge open on the score lines 24, 36 and 56 which are in a commmon vertical plane passing through a diameter of the bottom wall. The bottom wall panels are locked in position by engagement of the hook formations or locking fingers 13 and 23', on the connected pair of panels 20 and 27, in the cooperating locking apertures 59 and 39, respectively, the latter being located in the panels 52 and 32 at a predetermined distance from the intersection of the score lines 11 and 12 with the hinge line 14 and along the score lines 56 and 36, respectively. The locking apertures 59 and 39 are spaced along the score lines 56 and 36 so that when the locking tongues or fingers 23 and 23 are engaged therein the bottom wall assumes an upwardly bulging orcone-shaped contour, as shown in FIG. 2, and with the resiliency of the panel material provides a cushion bottom for supporting the contents. This arrangement adapts the container particularly for packaging products, such as, potato chips or the like, resulting in less breakage of the product in the bottom portion of the container.

The bottom wall forming panels 20, 27, 30, 32, 42 and 52 are connected along the chord-like, straight hinge lines 21, 28, 31, 33, 43 and 53 to the bottom edges of the web formations 73, 76, 72, 74, 75 and 71 in the bottom margins of the side walls which web formations are flat at the hinge lines and extend upwardly and merge into the round contour of the container body along the upwardly bowed semi-circular fold lines 67, 70, 66, 68, 69 and 65. The desired fold lines may be obtained by means of the score lines, as illustrated, or by relatively short pairs of straight converging score lines extending from the ends of the respective bottom hinge lines 21, 28, 31, 33, 43 and 53, or by any other means which will provide the desired uniform contour.

The cone-shaped bottom wall contour may be varied by adjusting the location of the locking apertures along the fold lines 36 and 56, it being possible to obtain a flat bottom contour with proper location of the locking apertures. The locking members 23 and 23' have an arrow head shape and a maximum width greater than the diameter of the semi-circular apertures or openings 39 and 59. They enter the apertures in partially opened up condition and pass through the slits 41, 41 and 61, 61' for full engagement as shown in FIG. 4 when the container is set up. The set up container may be collapsed by reverse movements and disengagement of the locking members 23 and 23' from the apertures 39 and 59 in the panel members 32 and 52.

I claim:

1. A collapsible container formed from a blank of foldable sheet material which is cut, creased and connected so as to provide, when set up, a tubular body and a bottom closing end wall, the body comprising a pair of rectangular side wall forming panels joined at corresponding ends along parallel, axially extending, hinge forming crease lines so that the panels may be collapsed upon each other into flattened coplanar relation, said body having a circular cross section at the open end, when opened up, so as to receive a cover having a circular periphery for closing said open end, said bottom end wall comprising a plurality of pairs of closure forming panels which are connected along straight hinge lines to the bottom edge of the side wall, one of the panels of each of said pairs of panels having a connecting flap which is hinged on a common diametrical line in the set up position of the container and connected to the other panel of said pair whereby when the container is collapsed the panels of each of said pairs of said bottom closure forming panels collapse upon each other inwardly of the bottom edges of the side wall panels so as to be disposed between the side wall panels when the side wall panels are collapsed, the panels of each of said pairs of bottom closure forming panels being connected so as to open up automatically into bottom wall forming position when the side wall panels are opened up into tubular form, one of the panels of one pair of said bottom end wall closure forming panels having locking tongue elements extending from opposite side edges and one panel of each of the pairs of panels adjoining said tongue bearing panel having a locking aperture therein for interengaging cooperation with one of said locking tongue elements so as to interlock said panels in predetermined bottom end wall forming position.

,2. A collapsible container as set forth in claim 1 wherein said locking elements comprise locking fingers on said one bottom end wall forming panel and wherein said cooperating locking apertures for receiving said locking fingers are disposed in marginal portions of said adjoining bottom end wall forming panels and in spaced relation from free edges of said adjoining panels, which locking fingers and apertures straddle said diametrical hinge line.

3. A collapsible container as set forth in claim 1 wherein said pairs of bottom end wall forming panels have free marginal portions substantially overlapping each other in the set-up position.

4. A collapsible container as set forth in claim 3 wherein said bottom end wall forming panels fold on hinge lines which are in a common vertical plane passing through a diameter of said bottom end wall and said axially extending hinge lines.

5. A collapsible container as set forth in claim 1 wherein one of said pairs of bottom end wall forming panels comprises generally rectangular panels hinged to opposite bottom edge portions of said side wall forming panels and foldable on a diametrical hinge line with said locking elements in the form of locking finger members extending on opposite side edges of said one rectangular panel which straddle said diametrical hinge line and which interlock with cooperating locking apertures in the adjoining pairs of bottom wall forming panels which also straddle said diametrical hinge line and hold said pairs of panels in bottom wall forming position.

6. A collapsible container as set forth in claim 1 wherein said pairs of bottom end wall forming panels are dimensioned and said locking elements are positioned so as to hold said bottom wall forming panels in upwardly directed coneshaped formation.

7. A collapsible container formed from a cut and scored blank of paperboard or similar foldable sheet material which, when set up, provides a collapsible tubular body having an end wall closure structure which comprises a plurality of panels integrally hinged along straight lines to the bottom edge of the tubular body, which end wall panels are connected in pairs and the panels of each pair thereof are collapsible on a hinge line which is on a common diametrical line in the set up position of the container with each pair thereof having portions which overlap portions of an adjoining pair thereof when in the set up position, whereby the panels automatically fold inwardly between the body side wall forming panels when the latter are collapsed and, when the container is opened up, said pairs of panels automatically move to end wall closure forming position, said overlapping portions of said end wall panels having locking fingers and co-operating locking apertures spaced along said common hinge line which automatically move in a direction along said hinge line into aligned relation and which interlock when said closure panels are moved outwardly to predetermined nonplanar position where the end wall panels are held in locked, inwardly bulging, generally cone-shaped, end

wall formation and provide a support for the container contents which has a degree of resiliency.

8. A collapsible container formed from a blank of foldable sheet material which is cut, creased and connected so as to provide, when set up, a tubular body and a closure forming end wall, the body comprising side wall forming panels joined by hinge forming crease lines so that the panels may be collapsed upon each other into flattened coplanar relation, said end wall comprising pairs of closure forming panels which are connected along straight hinge lines to the end edge of the side wall, one of the panels of each pair thereof having a connecting flap which is hinged on a common diametrical line in the set up position of the container and connected to the other panel of said pair whereby when the container is collapsed the panels of each pair collapse upon each other inwardly of the end edges of the side wall panels so as to be disposed between the side wall panels when the side wall panels are collapsed, said closure forming panels opening up automatically and moving into end wall forming position when the side wall panels are opened up into tubular form, and said end wall forming panels having locking elements which comprise locking fingers in the form of an arrowhead extending outwardly of opposite side edges of one of said pairs of closure forming panels and straddling said diametrical line, and cooperating locking apertures spaced inwardly of the free edges of pairs of closure forming panels which are disposed, when opened up, in partially overlying relation along opposite side edges of said pair of closure panels having said locking fingers, which locking apertures straddle said diametrical line and are located so as to move automatically into position to receive said locking fingers as said closure forming panels open up into end wall forming position.

9. A collapsible container as set forth in claim 8 wherein said end wall forming panels fold on hinge lines which are in a common vertical plane passing through a diameter of said bottom end wall and said axially extending hinge lines.

10. A collapsible container as set forth in claim 8 wherein said pairs of end wall forming panels are dimensioned and said locking elements are positioned so as to hold said end wall forming panels in a generally cone-shaped formation bulging inwardly of said tubular body. 

1. A collapsible container formed from a blank of foldable sheet material which is cut, creased and connected so as to provide, when set up, a tubular body and a bottom closing end wall, the body comprising a pair of rectangular side wall forming panels joined at corresponding ends along parallel, axially extending, hinge forming crease lines so that the panels may be collapsed upon each other into flattened coplanar relation, said body having a circular cross section at the open end, when opened up, so as to receive a cover having a circular periphery for closing said open end, said bottom end wall comprising a plurality of pairs of closure forming panels which are connected along straight hinge lines to the bottom edge of the side wall, one of the panels of each of said pairs of panels having a connecting flap which is hinged on a common diametrical line in the set up position of the container and connected to the other panel of said pair whereby when the container is collapsed the panels of each of said pairs of said bottom closure forming panels collapse upon each other inwardly of the bottom edges of the side wall panels so as to be disposed between the side wall panels when the side wall panels are collapsed, the panels of each of said pairs of bottom closure forming panels being connected so as to open up automatically into bottom wall forming position when the side wall panels are opened up into tubular form, one of the panels of one pair of said bottom end wall closure forming panels having locking tongue elements extending from opposite side edges and one panel of each of the pairs of panels adjoining said tongue bearing panel having a locking aperture therein for interengaging cooperation with one of said locking tongue elements so as to interlock said panels in predetermined bottom end wall forming position.
 2. A collapsible container as set forth in claim 1 wherein said locking elements comprise locking fingers on said one bottom end wall forming panel and wherein said cooperating locking apertures for receiving said locking fingers are disposed in marginal portions of said adjoining bottom end wall forming panels and in spaced relation from free edges of said adjoining panels, which locking fingers and apertures straddle said diametrical hinge line.
 3. A collapsible container as set forth in claim 1 wherein said pairs of bottom end wall forming panels have free marginal portions substantially overlapping each other in the set-up position.
 4. A collapsible container as set forth in claim 3 wherein said bottom end wall forming panels fold on hinge lines which are in a common vertical plane passing through a dIameter of said bottom end wall and said axially extending hinge lines.
 5. A collapsible container as set forth in claim 1 wherein one of said pairs of bottom end wall forming panels comprises generally rectangular panels hinged to opposite bottom edge portions of said side wall forming panels and foldable on a diametrical hinge line with said locking elements in the form of locking finger members extending on opposite side edges of said one rectangular panel which straddle said diametrical hinge line and which interlock with cooperating locking apertures in the adjoining pairs of bottom wall forming panels which also straddle said diametrical hinge line and hold said pairs of panels in bottom wall forming position.
 6. A collapsible container as set forth in claim 1 wherein said pairs of bottom end wall forming panels are dimensioned and said locking elements are positioned so as to hold said bottom wall forming panels in upwardly directed cone-shaped formation.
 7. A collapsible container formed from a cut and scored blank of paperboard or similar foldable sheet material which, when set up, provides a collapsible tubular body having an end wall closure structure which comprises a plurality of panels integrally hinged along straight lines to the bottom edge of the tubular body, which end wall panels are connected in pairs and the panels of each pair thereof are collapsible on a hinge line which is on a common diametrical line in the set up position of the container with each pair thereof having portions which overlap portions of an adjoining pair thereof when in the set up position, whereby the panels automatically fold inwardly between the body side wall forming panels when the latter are collapsed and, when the container is opened up, said pairs of panels automatically move to end wall closure forming position, said overlapping portions of said end wall panels having locking fingers and co-operating locking apertures spaced along said common hinge line which automatically move in a direction along said hinge line into aligned relation and which interlock when said closure panels are moved outwardly to predetermined non-planar position where the end wall panels are held in locked, inwardly bulging, generally cone-shaped, end wall formation and provide a support for the container contents which has a degree of resiliency.
 8. A collapsible container formed from a blank of foldable sheet material which is cut, creased and connected so as to provide, when set up, a tubular body and a closure forming end wall, the body comprising side wall forming panels joined by hinge forming crease lines so that the panels may be collapsed upon each other into flattened coplanar relation, said end wall comprising pairs of closure forming panels which are connected along straight hinge lines to the end edge of the side wall, one of the panels of each pair thereof having a connecting flap which is hinged on a common diametrical line in the set up position of the container and connected to the other panel of said pair whereby when the container is collapsed the panels of each pair collapse upon each other inwardly of the end edges of the side wall panels so as to be disposed between the side wall panels when the side wall panels are collapsed, said closure forming panels opening up automatically and moving into end wall forming position when the side wall panels are opened up into tubular form, and said end wall forming panels having locking elements which comprise locking fingers in the form of an arrowhead extending outwardly of opposite side edges of one of said pairs of closure forming panels and straddling said diametrical line, and cooperating locking apertures spaced inwardly of the free edges of pairs of closure forming panels which are disposed, when opened up, in partially overlying relation along opposite side edges of said pair of closure panels having said locking fingers, which locking apertures straddle said diametrical line and are located so as to move automatically iNto position to receive said locking fingers as said closure forming panels open up into end wall forming position.
 9. A collapsible container as set forth in claim 8 wherein said end wall forming panels fold on hinge lines which are in a common vertical plane passing through a diameter of said bottom end wall and said axially extending hinge lines.
 10. A collapsible container as set forth in claim 8 wherein said pairs of end wall forming panels are dimensioned and said locking elements are positioned so as to hold said end wall forming panels in a generally cone-shaped formation bulging inwardly of said tubular body. 